Since nitrogen mustard was clinically used as an antineoplastic drug in the 1940s for the first time in the world, many antitumor drugs have been developed until now. Many of these antitumor drugs, however, can also exhibit cytotoxic action to normal cells, and thereby can show severe side-effects such as gastrointestinal dysfunction, myelosuppression, and hair loss. Therefore, most of these antitumor drugs are limited to the usage, and often show partial and short-term effects. Along with the recent developments in molecular biology, it has been tried to identify more highly tumor-selective molecular targets to improve the effect and side-effect, and such trials have attained some progress. However, the positive effects are not so expected in tumors which have low express/contribution of molecular targets, and the side-effects are not low as desired. Thus, it has been desired to develop novel drugs.
Some antitumor drugs having a phenyldihydropyridazinone moiety which the present invention comprises are known, but all those structures are different from that of the present invention (Patent Literature 1 and Patent Literature 2).